Dom,
I've been testing some sheet stock Neoprene from McMaster-Carr and pre-soaking it with Aerospace Protectant from 303 Products. So far so good; however, I'm not so sure the protectant is saving it. I have a sneaking suspicion that the "rubber" composition of all these various weatherstrips is where the problem lies.
The "rubber" gaskets Specter sells for the later front turn signals deteriorates within a year, as well as their aftermarket tie-rod boots. And expensively, I have learned that the specialized OEM weatherstrip--which is no longer available-- that fits around the edge of the later cowl vent air flap, has hardened into a worthless crispy mess after a year or so as well.
I do agree, that for the most part the original factory "rubber" parts last the longest, as proven by their 40+ years in-use. But I don't agree that ALL of the original stuff is best--the aftermarket dash padding which is blended with a UV chemical, seems to hold up better to the sun--at least for now.
Considering that you cannot replace some of the weatherstrips with unavailable OEM products, I also am holding back installing any of those treasures until the projects are painted and complete-- simply making-do with home-made knockoffs, or in the case of door seals, nothing at all until that day. It gets mighty cold when driving in the snow, though !
If you can find the name of the PROVEN longest-lasting "rubber" material for manufacturing replacement parts, and then take a poll of interested prospective buyers, please add me to your list. But beware some of the third-world overseas offers to replicate stuff. Many of them use a pure rubber compound which may, in their home country, hold up well to the elements. However, with our ozone & industrial pollutants adding to the increased UV, real rubber may not be the wisest choice. Adding that to the green-weenie restrictions on chemical use here in Kalifornia, maybe another state may be the better choice for manufacturing.
One last thing. If the original Toyota parts held up so well in the past 40 years, but now seem to deteriorate faster than before, what the heck is happening to us--our skin, lungs, etc.. Maybe I should put in for a few good replacement parts now, before all mine wear out before I finish my resto projects !
It sure seems like it should last longer than that, right? My truck lives by the beach but is stored in the garage. 
